The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Homogenous charge compression ignition (HCCI) engines combust an air/fuel mixture within cylinders to push pistons toward bottom dead centre (BDC), thereby producing drive or mechanical torque. At low to medium engine loads and low to medium engine speeds (RPMs), the air/fuel mixture is automatically ignited when compressed by the pistons (i.e., an HCCI engine system is operating in an auto-ignited, or HCCI, combustion mode). Otherwise, the air/fuel mixture is ignited via spark plugs (i.e., the HCCI engine system is operating in a spark-ignited combustion mode). The HCCI combustion mode improves efficiency and fuel economy of the engine.
Engine control systems have been developed to control combustion (e.g., to manage air/fuel charge and ignition timing) to achieve the HCCI and the spark-ignited combustion modes. The HCCI combustion mode is limited to low and medium engine loads to protect the engine from damage due to rapid pressure increases and to limit combustion noise created by the engine. Traditional engine control systems, however, do not limit combustion noise as accurately as desired. For example, in those systems, the HCCI combustion mode is not limited by ambient conditions (i.e., barometric pressure, temperature, and humidity) and fuel type, which may vary combustion noise.